John Brennan apologised to the Senate's intelligence committee leaders after his inspector general found CIA employees acted improperly when they searched Senate computers earlier this year.

Agency spokesman Dean Boyd said Brennan has put together an accountability board that will investigate the conduct of the CIA officers and discipline them, if necessary.

The Justice Department has so far declined to pursue criminal charges against the employees, who searched the computers for information gathered in the course of an investigation into the CIA's interrogation techniques.

The controversy is centred on an investigation of the CIA's interrogation and detention practices after the September 11, 2001 attacks against the US.